Thixoforming : Semi-solid Metal Processing

Figure 1.12 Substituting original forged steel steering
knuckle (weight 3.2 kg) by A357 semi-solid casting (weight
1.5 kg) [44].
1.3 Today s Technologies of Semi-solid Metal Formingj19
cost–performance relation, successful serial applications make use of the specific
superior properties of semi-solid formed components to compensate for the additional
costs involved. Examples of such applications include pressure-tight components
such as fuel rails (Magneti Marelli), automotive structural chassis and
suspension components such as steering knuckles and connecting rods (Stampal),
taking advantage of the high mechanical properties, or front door pillars (SAG),
requiring close tolerances and high weldability.
One difficulty when introducing the semi-solid metal (SSM) process is that usually
it is not sufficient to substitute only the process for a given part geometry. In most
cases a process-specific redesign will be required to achieve substantial benefits. This
especially holds if the goal is to achieve significant weight savings, that is, by
substituting steel forging by semi-solid forming of aluminium. As an example,
Figure 1.12 shows the redesign of a forged steering knuckle [44]. The new design uses
the process capabilities of semi-solid casting and reduces weight by creating hollow
cross-sections with high stiffness, which is not possible in forging. The component,
which has been semi-solid cast in A357 alloy, fulfilled all dynamic testing procedures
that were required for this component while reducing the part weight to 50% of the
original steel solution.
1.3.5.2 Other Aluminium Alloys
Even though the broad range of mechanical properties achievable by the AlSi7Mg
alloys covers many technical fields, some applications require specific properties
which could be better achieved by other alloy systems. This has led to various alloy
developments and demonstration tests to exploit the potential of semi-solid forming